Gasoline marine engines used in small water craft are typically of two types. A first type is an inboard mounted engine which drives a propulsion unit which may be an outboard mounted propeller or jet. A second type of gasoline marine engine used in small water craft is an outboard engine that mounts high on the transom of the boat. There are significant problems with both types of marine engines.
Inboard engines comprise all types of engine block configurations including V-Block and straight block or in-line engine blocks. Additionally, a small number of gasoline marine engines have been built using an engine block having horizontally opposed cylinders.
These gasoline marine engines are either designed specifically for marine usage or are of automobile origin and have undergone a significant conversion to make the engines appropriate for marine usage. For an engine to be appropriate for marine usage, the engine must satisfy the particular cooling requirements of mounting an engine within the hull of the boat. Specifically, a cooling system is required that will not use a radiator and fan for transferring the heat within the engine coolant to the atmosphere. Additionally, the cooling provided by air passing through the engine compartment of a car will not be present. Automobiles rely heavily on the radiator and fan and air cooling to keep the engine from overheating. Due to the constraints that are particular to mounting an engine within a hull of a small water craft, neither of these cooling modes are typically used on a boat engine.
Consequently, gasoline marine engines for small water craft must include greater engine cooling capabilities. Greater cooling capabilities are required of the water jackets that are cast into the cylinder blocks and cylinder heads. Additionally, cooling capabilities are also required of the exhaust system. Exhaust jackets are typically placed around the exhaust system manifold and pipes to cools these components with cooling water. Water jackets and exhaust jackets, both of which are specifically designed for the cooling requirements of the marine environment, are required in gasoline marine engines.
Coolant systems for marine use are typically of two types. A first system uses a heat transfer mechanism that uses raw water drawn from the water resource to cool the engine coolant used within the water jackets. Alternatively, raw water may in some cases be drawn from the water resource and then passed through the water jackets, and finally returned to the water resource. In each of these systems, raw water, as opposed to air, is used to cool the coolant fluid is used in the engine.
Because of space limitations marine engines are typically not used with a shiftable transmission. The propulsion system is typically driven directly by the flywheel of the engine.
In common jet propulsion systems, the jet impeller speed in RPM's is the same as the engine speed in RPM's. The impeller speeds that result are typically desirable for higher speed boat usage. Most boat engines are unable to run under 500 revolutions per minute, and therefore are driving the impellers at too high of a speed for low speed boating without the difficult use of the reverse bucket to slow the boat speed. These engines also do not allow for the desired level of speed modulation for the boat.
Propeller propulsion systems typically use a gear reduction system. In these systems, the propeller speed is a constant percentage of the engine RPM, as these systems also do not permit any change of the gearing while the boat is operating. These gear reduction systems seldom allow for low enough propeller speeds for low speed fishing which is commonly called trolling. This is because the systems are typically geared for higher speed use. For this reason, a propeller specifically designed for low speed operation must typically be used if low speed operation is desired. These low speed propellers drastically reduce the top end speed of the boat and are not considered desirable by most boat users.
For these reasons, those boat users that desire to operate their boats at trolling speeds are required to install a small trolling engine on their boats. The trolling engine capable of low speeds only becomes the second engine for the boat. These small trolling engines, which are typically outboard engines mounted on the transom of the boat, allow the user to have a high level of modulation control over the boat speed. The use of two engines on a boat is not without consequence, however. Two marine engines often means a doubling of the undesirable maintenance requirements of the boat. There are, of course, additional costs involved in the acquisition of a second engine for the boat. A second engine mounted on the transom also occupies one of the desirable fishing positions available within the hull of the boat.
The other option for low speed of an existing gasoline marine engine is to fit a trolling plate adjacent the propeller that can be pivoted behind the propeller to slow the propulsion of the boat. The use of these trolling plates is undesirable as little modulation of speed is possible. The operation of the trolling plates is also undesirably inconvenient. It is also likely that the use of a trolling plate generates a high level of underwater noise due to the constant striking of water on the plate. This likely would scare away fish from the vicinity of the boat.
Existing inboard gasoline marine engines, in the lower horse power classes, also lack the necessary torque at low speed to push the boat up on plane if the boat is carrying a heavy load of passengers and gear. For boat users that fish in large rivers and rivers with a strong current, there may be considerable frustration involved in getting the boat to move upstream if the boat cannot generate enough low speed torque. Several fishermen and their gear can add a significant load to a small water craft. It is not uncommon for existing gasoline marine engines for small water craft to be inadequate under these conditions.
Larger horsepower inboard gasoline marine engines have the necessary torque for most applications. However, these larger horsepower engines are quite massive, often weighing 900 pounds or more. Of course, the fuel consumption of these engines is also high. This reduces the operating range of the boat and increases the necessary fuel storage and therefore the weight of the fuel on the boat.
An additional problem associated with existing inboard gasoline marine engines of all horse power classes is the size, particularly the height, of the engine. The decks of small water craft have space for seating and gear storage. Unfortunately, the main inboard engine occupies a significant portion of this space at the rear of the boat in front of the transom. The engine typically includes a cover to separate the engine from the interior of the boat. The height of the cover which extends over the engine is typically too high for comfortable or safe seating. Additionally the engine cover restricts the ability of the number of people that can stand at the back of the boat and fish. This position at the back of the boat is typically the most desirable place from which to fish. Due to the shape of existing marine engines for small water craft, very few marine engines have been successful at minimizing the space requirements of an inboard engine.
Existing outboard marine engines also have had significant problems. Most existing outboard engines are two stroke engines that are know to be responsible for extremely high emissions of unburned hydrocarbons, as well as other atmospheric pollutants. Outboard engines also require higher levels of maintenance than inboard engines of comparable horsepower. Although outboard engines do minimize the deck space which the engine occupies, outboard engines do extend quite high above the transom and are an obstruction to using the back of the boat for fishing. The location of outboard engines also has a tendency to increase the noise level within the boat due to the engine.
For the previously mentioned reasons, there is a need for an inboard gasoline marine engine for small water craft that develops sufficient torque to function adequately at low speeds. There is a need that this engine weighs much less than existing engines which are able to produce a high torque at low speeds. This would provide adequate boat operation in river currents, and adequate operation of the boat if the boat is loaded down with people and gear.
There is a farther need for a single inboard gasoline marine engine for small water craft that will operate at very low speeds without stalling so that the single marine engine can be used for low speed trolling. There is a need that this engine also offers the boat operator a high level of speed modulation. There is a need that this engine also has performance characteristics suitable for higher speed boat use.
There is a need that this inboard gasoline marine engine for small water craft be of a minimal height so as to occupy a minimum of deck space in the boat. It would be advantageous that this marine engine would fit under a platform or seat located in front of the transom, or actually fit beneath the deck. This would ensure that a maximum of deck space is available to be fully used by the boat occupants.
There is a need that this inboard gasoline marine engine for small water craft operates with very low polluting exhaust emissions to ensure that minimal harm to water sources and the atmosphere results from using the boat. There is also a need that this engine operates with minimal noise levels. Finally there is a need that the engine operates in a reliable manner and requires a minimum of maintenance.